In the field of the medical image diagnosis, there has been an increasing demand in recent years for diagnosing the interior of an object by taking a three-dimensional image of the object for observation, not excepting the field of ultrasonic diagnosis. The diagnosis using three-dimensional images has been developed especially in the field of the X-ray CT apparatus using X-rays and of the magnetic resonance imaging apparatus using nuclear magnetic resonance. But, the development of three-dimensional imaging has been delayed in the field of the ultrasonic diagnosis because an ultrasonic diagnostic apparatus performs scanning with ultrasonic beams having a propagation velocity in a living body which is as slow as approximately 1,500 m/s, and so it takes a long time to take a three-dimensional image of the interior of an object, since such a three-dimensional image requires a far greater number of beams, in comparison with a conventional cross sectional image that is made from approximately 100 beams.
Further, to perform three-dimensional scanning with ultrasonic beams in the object, a method of manually or mechanically moving a probe having one-dimensional built-in transducers on the surface of the object has been proposed. However, it is difficult to actually use this method, since the surface of the object is uneven, which is a second reason for the delay of development of the ultrasonic three-dimensional imaging.
As described above, the propagation velocity of ultrasound in a living body is approximately 1,500 m/s, and so a conventional cross-sectional image of the examined region can be displayed at a frame rate of 30 frames/s. Here, the number of ultrasonic scanning lines used for forming the cross sectional image is about 100. If a three-dimensional image is to be obtained with 100 scanning lines, it is necessary to narrow the scanning area, or to expand the interval between scanning lines if the scanning area is not narrowed. However, even if these methods were employed in an ultrasonic diagnostic apparatus, this apparatus could not be used for an actual diagnosis. To perform high-speed scanning on the object in real time, there are proposed a method of obtaining several beams to be received with one transmission of one ultrasonic beam and a method of transmitting ultrasonic beams in several directions at one time. However, there is a limit to the increase in processing speed obtainable by the former method. In the latter method, there is a problem that one ultrasonic beam interferes with another beam if the simultaneously transmitted beams approach each other; that is, there is a problem in that a transducer or a group of transducers may receive a reflected wave of the ultrasonic beam transmitted by the adjoining transducer or group of transducers. Therefore, the above-described conventional technology has not achieved the objective to perform three-dimensional measurement using ultrasonic beams in the object at rapid speed.
However, since various kinds of methods of producing a two-dimensional probe using a fine processing technology have been recently developed, it is becoming possible to perform three-dimensional scanning with ultrasonic beams in an object by using an electrical scanning method, without moving the probe on the surface of the object.
In the conventional technology, as described above, it takes a very long time to perform a measurement by three-dimensional scanning using ultrasonic beams in an object. The object cannot move throughout the measurement, which puts a great burden on the object. Moreover, it is difficult to observe a three-dimensional image in real time, since the procedure requires a long measurement time. These problems have not been solved at this stage of development, and an early solution of them is desired.
The present invention has been made in consideration of the above-described circumstances. The first object of the present invention is to provide an ultrasonic diagnostic apparatus that can perform three-dimensional scanning with ultrasonic beams at rapid speed.
And, the second object of the present invention is to provide an ultrasonic diagnostic apparatus that can promptly display an ultrasonic three-dimensional image.